. >> reporter: piece by piece inside this ntsb lab in washington, analysts are dissecting the charred battery which caught on fire in a boeing 787 dreamliner earlier this month in boston. >> we know that the lithium ion battery experienced a thermal runaway. we no that there were short circuits, and we know that there was a fire. >> reporter: the faa gave special permission to boeing, allowing the use of these light weight batteries only if safety measures were installed to prevent overheating. >> we do not expect to see fire events on board aircrafts. there are multiple systems to protect against a battery event like this. those systems did not work as intended. we need to understand why. >> reporter: the investigation was launched after two 787s this month experienced issues surrounding the jet's unique use of lithium ion batteries. fais battery behind the wings of a japan airlines 787 exploded and caught fire while on the ground in boston. initial tests rule out excess voltage and overcharging. another battery problem, this one near the cockpit of an all nippon airways dreamliner l